RFR: 8320112 GenShen: Improve end of process report [v2]

[Kelvin Nilsen]

On Tue, 14 Nov 2023 23:14:48 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> When Shenandoah is shutdown, it logs a summary of its activity over the life of the process. This change adds percentages to the breakdown of the types and counts of cycles that executed. It also simplifies some of the logic around recording the various outcomes.
>
> William Kemper has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Reduce visibility of new methods
>  - Fix accidental whitespace change

I haven't digested all the control paths.  Some of the changes make me a bit nervous.  When degen young "upgrades to full", we have special handling.  For example, we update the live-at-end-of-last-old-mark variable, and we reset the count of consecutive degenerated cycles.  Do these changes preserve both of those behaviors?

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PR Review: https://git.openjdk.org/shenandoah/pull/357#pullrequestreview-1731105463